Microcytic anemia is one of the most common problems faced in the primary care physician’s office, and for many patients is synonymous with iron deficiency anemia.  In fact the most common cause of microcytic anemia is iron deficiency, and in low risk patients physicians often confirm the diagnosis of iron deficiency as the cause by a good response to iron therapy.   That said, there are other important and fairly common causes of microcytic anemia that physicians keep in mind when they see a patient with this condition.

Anemia is a condition where the amount of hemoglobin in the bloodstream at levels lower than is considered normal.  Anemia is broken down into three major groups based on the size of the red blood cells.  Normocytic anemia is when the red blood cells are of normal size.  This is from 80-100 microns in diameter, and is measured as the MCV, or mean corpuscular volume on the usual complete blood count done by automated hemocytometers in most labs.  Macrocytic anemia is when the red blood cell size is larger than normal, i.e.an MCV of >100.  B12 deficiency is one of the common causes of macrocytic anemia. Microcytic anemia is when the red blood cells are smaller than normal, i.e. the MCV <80.

When iron deficiency is diagnosed as  the cause of a petient’s microcytic anemia, the most important task is to discover why the patient is iron deficient.  The  cause can be either poor intake or absorption of iron from the diet, or loss of iron in blood cells lost from apparent or occult bleeding.  Most cases of blood loss iron deficiency are from intestinal blood loss form conditions like ulcers, gastritis, esophagietis, or from the colon from colon polyps, cancer, or angiodysplasia.  IN women of childbearing age menstrual blood loss is another common cause of iron deficiency.

Treatment of iron deficiency is usually easily accomplished with oral iron supplementations.  IN rare cases iron needs to be given intravenously, but this route risks serious allergic reactions and is avoided when possible.

Lead poisoning is the next most common and one of the most serious causes of microcytic anemia.  It needs to be suspected in any young child with microcytic anemia who does not respond quickly to iron supplementation, or who lives in a home with lead pain exposure.  This is mostly older homes

Anemia of chronic disease is another cause of microcytic anemia.  Usually this anemia is normocytic, but in a minority of cases an anemia of chronic disease can be microcytic.   This type of anemia is common inpatients on dialysis or with significant chronic renal insufficiency, or other patients with serious chronic medical problems.

Sideroblastic anemia is the last fairly common cause of microcytic anemia.  IT occurs in patients with serious bone marrow disease, often premalignant or early leukemia or myelodysplasia.

If you have anemia, the first thing your physician is likely to look at is your MCV to assess whether you have a microcytic, normocytic, or macrocytic anemia, and will decide on further testing from there.

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